Food PreservationChapter 27

Food Spoilage

Biological Changes

• Fermentation: The conversion of carbohydrates to carbon dioxide and alcohol by yeast or bacteria.

Food Spoilage

Chemical Changes

• Enzymes play a significant role in catalyzing these reactions– Proteases, also called

proteolytic enzymes, split proteins into smaller compounds.

Food Spoilage

Physical Changes

The most common physical changes occurring in foods as they spoil are evaporation, drip loss, and separation.

• Dehydrate: To remove at least 95% of the water from foods by the use of high temperatures.

• Freeze-dry: To remove water from food when it is in a frozen state, usually under a vacuum.

Food Preservation Methods• Drying is the food

preservation process that consists of removing the food’s water, which effectively inhibits the growth of microorganisms. Like:– Sun Drying

Food Preservation Methods

Commercial Drying • The most important types of

commercial drying are: –Conventional: heat.–Vacuum: pulls the water out.–Osmotic: water drawn out by

osmosis.–Freeze-drying: ice crystals

vaporize.

Food Preservation Methods

Sublimation: The process in which a solid changes directly to a vapor without passing through the liquid phase.

Food Preservation Methods• Cure: To preserve food through the use

of salt and drying. Sugar, spices, or nitrates may also be added.

• Fermentation• Pickling uses vinegar to preserve foods.• Edible coating: Thin layer of edible

material such as natural wax, oil, petroleum-based wax, etc. that serves as a barrier to gas and moisture.

Food Preservation Methods• Carbohydrates

are required for the fermentation process.

• Throughout Asia, vegetables are still commonly fermented.

• In North America, foods most often preserved by fermentation are cucumbers, olives, and cabbage.

Food Preservation MethodsThe purpose of edible coatings is fourfold:

1. To increase shelf life by acting as a barrier to moisture, oxygen, carbon dioxide, volatile aromas, and other compounds whose loss would lead to deterioration.

2. To impart improved handling characteristics, such as the ability to bend more easily without breaking.

3. To improve appearance through increased gloss and color.

4. To serve as a vehicle for added ingredients such as flavors, antioxidants, antimicrobials, etc.

Food Preservation Methods• Canning is a two-step process:

– First the food is prepared by being packed into containers, which are then sealed.

– Then the containers are “canned,” or heated to ensure that all microorganisms are destroyed.

• Sterilization: The elimination of all microorganisms through extended boiling/heating to temperatures much higher than boiling or through the use of certain chemicals.

Cold Preservation

• Refrigeration slows down the biological, chemical, and physical reactions that shorten the shelf life of food.

• All perishable foods should be refrigerated as soon as possible, preferably during transport, to prevent bacteria from multiplying.

Cold Preservation

• Freezing makes water unavailable to microorganisms.

• The chemical and physical reactions leading to deterioration are slowed by freezing.

• Freezer burn: White or grayish patches on frozen food caused by water evaporating into the package’s air spaces.

Heat Preservation• Pasteurization: A

food preservation process that heats liquids to 160°for 15 seconds, or 143°F for 30 minutes, in order to kill bacteria, yeasts, and molds.

• Ohmic heating: A food reservation process in which an electrical current is passed through food, generating enough heat to destroy microorganisms.

Other Preservation Methods

Irradiation: A food preservation process in which foods are treated with low doses of gamma rays, x-rays, or electrons.

Symbol for Irradiated Foods

(Green) Radura

Other Preservation MethodsHow is irradation is used:

• Sterilization of medical equipment (instruments, surgical gloves, alcohol wipes, sutures, etc.)

• Sterilization of consumer products (adhesive bandages, contact lens cleaning solutions, cosmetics, etc.)

• Foods for immune-compromised hospital patients (e.g., AIDS, cancer, or transplant patients)

• Some foods for astronauts, who cannot risk foodborne illness

• Spices and seasonings used in products such as sausage and certain baked goods

Other Preservation Methods

Pulsed Light exposes the food to intense, very brief flashes of light, which disrupt the cell membranes of bacterial cells, but not that of the surrounding food.

Other Preservation Methods

• High-pressure processing of foods inactivates foodborne microorganisms at low temperatures without the use of chemical preservatives.

• Pascalization: A food preservation process utilizing ultrahigh pressures to inhibit the chemical processes of food deterioration.

Other Preservation MethodsOzonation

• Ozone (an oxidizing agent) is commercially produced by exposing oxygen to an electrical current.

• Ozone is an effective disinfectant and sanitizer for many food products.

Other Preservation Methods

Aseptic and modified-atmosphere packaging (MAP)– Hermetically

sealed: Foods that have been packaged airtight by a commercial sealing process.